R.L. Myatt

The Levitated Dipole Experiment (LDX) magnet system

In the Levitated Dipole Experiment (LDX), a hot plasma is formed about a levitating superconducting dipole magnet in the center of a 5 m diameter vacuum vessel. The levitated magnet is suspended magnetically during an eight hour experimental run, then lowered and recooled overnight. The floating F-coil magnet consists of a layer-wound magnet with 4 sections, designed to wrap flux lines closely about the outside of the levitated cryostat. The conductor is a niobium-tin Rutherford cable, with enough stabilizer to permit passive quench protection. Lead strips are used as thermal capacitors to slow coil heating. An optimized system of bumpers and cold-mass supports reduces heat leak into the helium vessel. Airbags catch the floating coil on quenches and faults, preventing collision with the vacuum vessel.

TPX superconducting tokamak magnet system 1995 design and status overview

The TPX magnet preliminary design effort is summarized. Key results and accomplishments during preliminary design and supporting R&D are discussed, including conductor development, quench detection, TF and PF magnet design, conductor bending and forming, reaction heat treating, helium stubs, and winding pack insulation.

Superconducting magnets for Maglifter launch assist sleds

The Maglifter is an electromagnetic catapult being considered by NASA to reduce the cost of lifting a payload into space. The system would accelerate a vehicle of up to 590 tonnes to a final velocity of 268 m/s at an acceleration of 2 g. Superconducting coils are considered for levitation because they permit track-to-vehicle clearances of more than 95 mm. The high clearances reduce tolerances and maintenance costs, and allow a system with permanently deployed wheels for take- off and emergency landing. Cable-in-conduit conductors (CICC) were selected because of their high electrical and mechanical strength, as well as high energy margin for stability. The selected coil shape is a pair of racetrack coils forming a module with four modules on a sled. The superconducting levitation modules weigh about 4% of the gross lift off weight and are capable of achieving lift off at about 20 m/s. The maximum magnetic drag power is negligible compared to the power required for acceleration.

Eddy current heating in the cold structure in TPX

The toroidal field end cases and support structure for the TPX are at cryogenic temperatures. The time varying currents in the poloidal field coil system will induce eddy currents in these structures. The associated Joule dissipation will cause local heating and require heat removal which will show up as a load on the cryogenic system. Knowledge of the heat load distribution in both space and time is important to the design of the system. Analyses have been performed using programs EDDYCUFF and ANSYS and the results presented. >

Finite element analysis of the TPX toroidal field coil system

A structural analysis of the Tokamak Physics Experiment (TPX) toroidal field (TF) coil system is presented. The large-scale structural behavior of the superconducting 16-coil magnet is simulated with a 3-D, cyclically-symmetric, two-coil, ANSYS model. The computer model is used to determine the displacement and stress state of the smeared winding pack and support structure, and to perform various structural evaluations. Approximating the detailed stresses in the winding pack constituents based an smeared stress results and analytically derived component stress multipliers is discussed. The effectiveness of friction between wedged TF cases to help restrain out-of-plane electromagnetic forces is also considered. A stress evaluation of the conductor, insulation and structure is presented based on the TPX structural design criteria. >

Thermal analysis of the TPX TF coil case for eddy-current and neutron heating

A finite element, thermal analysis of the Tokamak Physics eXperiments (TPX) toroidal field (TF) coil case is presented. The analysis models the 316LN coil case as a 3-D shell with imposed thermal loads dominated by neutron and eddy current heating. Heat sinks which simulate the flow of supercritical helium in the coil case cooling system and adjacent conductor conduits are used to extract the steady-state heat load. The model is used to estimate the heat leak rate into the winding pack as input for heat removal and conductor temperature margin calculations. The proposed cooling scheme flows 5 K helium at 5 atmospheres to the TF coil winding packs. The effluent is directed into the case cooling channels. Results indicate that the case cooling system and ground wrap insulation are effective means of thermally isolating the superconductor from the heat deposited in the coil case; 92% of the 8.07 kW deposited in the cell cases by eddy currents and neutrons are extracted by the helium flowing in the case cooling channels while only 0.65 kW are transmitted into the adjacent conductors of the winding packs.<<ETX>>

Electromagnetic analyses of the GEM detector magnet system for SSC

The magnet system for the Superconducting Super Collider (SSC) Gamma, Electrons and Muons (GEM) detector consists of a single layer, superconducting, split solenoid and two iron forward field shapers (FFS). In addition, major structural components, such as the central detector and FFS support structures and the vacuum vessels, are to be built with magnetic steel. This paper presents the nonlinear, two and three-dimensional electromagnetic analyses which are performed in support of the overall design effort. A detailed axisymmetric, finite element ANSYS model is used to determine the magnetic field distribution in the region of the detector, and the electromagnetic forces acting on the coil and various magnetic steel elements. A 3-D model is developed to capture the magnetic field perturbations produced by asymmetric, magnetic structural elements. The model produces 3-D field maps of the detector volume to evaluate the effects of these asymmetries on the detector resolution. Another 3-D model is used to determine the distribution of magnetic steel plates required to shield the nearby Electronic Rack Room from the coils fringe field. >

The Advanced Hydrotest Facility (AHF) large bore quadrupole focusing magnet system

The Advanced Hydrotest Facility (AHF) at Los Alamos will provide proton radiography of large-scale, dynamic events. The large bore (Case II) quadrupole focusing magnets are a subsystem in this facility, consisting of four complete imaging lines with a total of eight imaging plates and 52 quadrupole magnets. Each large bore quadrupole has an inner winding diameter of 660 mm and provides a gradient of 10.4 T/m with a 300 mm field of view. Each magnet is a two-layer saddle, contained by a three cm steel shell. The conductor is a Rutherford cable, soldered into a C-shaped copper channel. The magnets are cooled by the forced-flow of two-phase helium through coolant pipes. Since the winding was calculated to absorb bursts of 0.35 J/kg irradiation, both NbTi and Nb/sub 3/Sn designs are being considered.

Coupled electromagnetic structural analysis of a DC magnet for a MHD power generator

A coupled electromagnetic and nonlinear structural analysis of a 4.5 tesla superconducting MHD dipole magnet is presented. The magnet design combines the latest in cable-in-conduit conductor (CICC) technology, a novel quasi-momentless support configuration, and finite element modeling to demonstrate the viability of this retrofit magnet concept. With the conductor participating as a major structural element, the support system is greatly simplified, and the overall cost and risk of the magnet system is reduced. Two and three-dimensional models are used to evaluate the concept and demonstrate how the full simulation is accomplished in one ANSYS computer run. >